Re: [PATCHv1 dont apply] RFC: kvm eoi PV using shared memory

Gleb Natapov
2012-04-17T09:10:40Z

On Mon, Apr 16, 2012 at 10:01:29PM +0300, Michael S. Tsirkin wrote:
> On Mon, Apr 16, 2012 at 08:51:16PM +0300, Gleb Natapov wrote:
> > > > Only when eoi is pending. This is rare.
> > >
> > > This is exactly while guest handles an interrupt.
> > > It's not all that rare at all: e.g. device
> > > drivers cause an exit from interrupt
> > > handler by doing io.
> > So eoi will be coalesced with io that device driver does. Exactly what
> > we want.
>
> It won't. While we handle interrupts eoi is still set.
> So there will be a couple of tests + read from userspace
> Wasted not a huge overhead but it's the principle of the thing.
>
Linux acks irq before calling device handler. Windows for some devices
does IO to a device before acking.

--
Gleb.